Heretofore in wide use as motor vehicle air conditioner evaporators are those of the so-called stacked plate type which comprise a plurality of flat hollow bodies arranged in parallel and each composed of a pair of dishlike plates facing toward each other and brazed to each other along peripheral edges thereof, and a louvered corrugated fin disposed between and brazed to each adjacent pair of flat hollow bodies. In recent years, however, it has been demanded to provide evaporators further reduced in size and weight and exhibiting higher performance.
To meet such a demand, the present applicant has already proposed an evaporator which comprise a heat exchange core composed of tube groups in the form of two rows arranged in parallel in the direction of passage of air and each comprising a plurality of heat exchange tubes arranged at a spacing, a refrigerant inlet-outlet tank disposed at the upper end of the heat exchange core and a refrigerant turn tank disposed at the lower end of the heat exchange core, the refrigerant inlet-outlet tank having its interior divided by a partition into a refrigerant inlet header and a refrigerant outlet tank arranged side by side in the direction of passage of air, the inlet header being provided with a refrigerant inlet at one end thereof, the outlet header being provided with a refrigerant outlet at one end thereof alongside the inlet, the refrigerant turn tank having its interior divided by a partition wall into a refrigerant inflow header and a refrigerant outflow header arranged side by side in the direction of passage of air, the partition wall of the refrigerant turn tank having a plurality of refrigerant passing holes formed therein and arranged longitudinally of the wall at a spacing, the heat exchange tubes of the front tube group having upper ends projecting into and joined to the inlet header, the heat exchange tubes of the rear tube group having upper ends projecting into and joined to the outlet header, the heat exchange tubes of the front tube group having lower ends joined to the inflow header, the heat exchange tubes of the rear tube group having lower ends joined to the outflow header. A refrigerant flowing into the inlet header of the inlet-outlet tank flows through the heat exchange tubes of the front tube group into the inflow header of the turn tank, then flows into the outflow header through the refrigerant passing holes in the partition wall and further flows into the outlet header of the inlet-outlet tank through the heat exchange tubes of the rear tube group (see the publication of JP-A NO. 2003-75024).
However, the present inventor has conducted extensive research and found that the evaporator disclosed in the above publication is likely to have the following problem because the inlet of the inlet header and the outlet of the outlet header are provided at the same end of the inlet-outlet tank, and further because the heat exchange tubes of the front group are joined to the inlet header with their upper ends projecting thereinto.
The portions of the heat exchange tubes projecting into the inlet header offer resistance to the refrigerant flowing in through the inlet, so that the refrigerant flowing into the inlet header encounters difficulty in flowing to a position remote from the inlet. Consequently, an increased amount of refrigerant flows into heat exchange tubes of the front tube group which are positioned close to the inlet to produce an increased refrigerant flow, while a reduced amount of refrigerant flows into heat exchange tubes positioned away from the inlet to produce a decreased refrigerant flow. Similarly in the rear tube group, heat exchange tubes positioned close to the inlet have an increased refrigerant flow, with a decrease in the refrigerant flow through those positioned away from the inlet. As a result, the amount of refrigerant flowing through the heat exchange core and contributing to heat exchange becomes uneven longitudinally of the inlet-outlet tank, and the air passing through the heat exchange core also becomes uneven at some location. Thus, the evaporator fails to exhibit fully improved heat exchange performance. This problem becomes more pronounced especially when the refrigerant flow rate is low.
An object of the present invention is to overcome the above problem and to provide a heat exchanger which is outstanding in heat exchange performance.